The trigeminal mesencephalic nucleus, main sensory nucleus, and rostral part of the spinal sensory nucleus of cats will be stereotaxically explored with extracellular microelectrodes to determine the location and firing patterns of single neurons which respond to passive movement of the condylar head of the mandible within the temporomandibular joint. Latency measurements will be made to determine the location of the cell bodies of first-order neurons by electronically stimulating the TMJ mechanoreceptors. The response patterns of these neurons will be analyzed with a digital computer. The analysis will be compared statistically with similar analyses derived from single neurons in the ventral posteromedial nucleus of the thalamus. This nucleus is thought to contain third-order projection neurons for kinesthesia of the temporomandibular joint. The results will be used to illuminate the mechanisms whereby mechanoreceptors in the temporomandibular joint single relative position of the jaw during masticatory movements.